Motivation

CHAPTER 1- I

This dissertation mainly focuses on the optimization of driving direct current brushless DC motor (BLDCM). The short introduction on research motivation which includes: new hardware architectures and software algorithms will be presented. The major contributions which include: new discovery and control strategy will be summarized. Finally, the detailed dissertation organization and structure will be described.

1.1 Motivation

Nowadays, energy saving and carbon reduction has become a part of life. Improving energy efficiency is a more important issue. The motor, which plays the important role of energy conversion, is indispensable in daily life. With a broad range of applications, it has more significant applications in aerospace, industries, automotive, household, and IT industry. More than half of the energy is consumed by the working motors. Therefore, using a high-efficiency motor to replace the traditional motor is an efficient way to save energy. For ultimate efficiency, high-efficiency motors need to know the rotor position in order to give the most appropriate commutation control, and the BLDCM driving control is the most simple control motor type of all high-efficiency drives. The BLDCM maintains the good dynamic and static characteristics of the velocity modulation of traditional DC motors, and it does not have the problems that brushes have, such as generating sparks due to friction in the structure or requiring periodic replacement due to brush wear. Hence, it has the characteristics of a simple structure and high reliability.

Technology advances have allowed power semiconductor technology to take a great leap forward which also launched the drive control for the BLDCM. The Hall elements have

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been created as a result of the discovery of the Hall effects. The rotor position detection of the BLDCM uses Hall elements to retrieve steady rotor position information. Because the structure of the BLDCM rotor is magnetic, the rotor position can be directly known from the Hall sensors. If optical encoding or other techniques are used, the installed devices create the disadvantage of a larger volume size. Therefore, at present, almost all BLDCM use a Hall sensor to detect the rotor position. However, in some occasions it is not suitable to install Hall sensors into motor because sensor elements will be affected by the harsh environment, resulting in more noise with the sensor signals or causing the sensor elements to fail. Therefore, use of the sensorless drive approach in this environment has the most substantial value.

The sensorless drives in BLDCM with more simple structures only connect the windings to the controller, so the controller can tolerate the poor environment and detect the commutation signals by the electrical characteristics of the windings. Currently, the BLDCM development is maturing in both sensor drive and sensorless drive technology.

There were a lot of technology papers discussing in the field of sensorless technology, but most of them focus on how to detect commutation information, and some discussed the phase correction methods. In practical, the phase correction problems were solved by using the method of building compensation tables. The BLDCM usually needs to associate with the controller in order to produce the best performance. For various types of motors, the BLDCM controllers often need to individually adjust the phase compensation value of the hardware circuit and the rotor position detection software to make the optimal adjustments. If the work of the compensation correction done by hardware or software can be reduced, the overall rate of product development will be greatly enhanced. Therefore, to uphold this kind of vitality, this dissertation proposes two kinds of technology: back electromotive force (BEMF) rotor detection circuit and

3 correspond to the BEMF. In addition, the angular position can be calculated through the relationship between the electrical cycle and the mechanical cycle, but these theoretical values tend to cause deviated because of post-processing or assembly. In addition, in order to prevent the interference or noise caused by the high temperature inside the motor from reaching the Hall sensors, frequently the magnetic rings of the same number as internal rotor’s magnetic poles are installed on the shaft core outside the BLDCM.

Through the magnetic poles of the magnetic sensor rings, the rotor position information can be retrieved. Such processing and installation is much more difficult compared to the direct positioning of Hall sensors in corresponding positions of silicon steel. Such institutions must rely on the drag platform to drag the motor for correction during installation so that rotation produces the BEMF, by which the Hall sensor is aligned. The other kind uses the rotor sensors that are being installed and let the motor drive at a low speed to find the minimum current point as the installation location. Such installation is very time consuming and inaccurate. So the installation of rotor position sensors so far is still a serious problem plaguing engineers. To solve these problems, this dissertation proposes a new design concept for a rotor position sensor auto-calibration system to automatically optimize the placement of Hall sensors and improve the current inability to verify the position of Hall sensors one by one before delivered from the factory.

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